Which Building Code Applies to a Rockford Basement?

The state baseline

Illinois has no single residential code run from Springfield. Since January 1, 2025 (Public Act 103-0510), a local code has to regulate structural design at least as strictly as the baseline codes:

“The baseline codes are the International Building Code including Appendix G, International Existing Building Code and International Residential Code, published in the current year or preceding nine calendar years.”

Statewide residential code baseline

The Illinois Municipal League summarises it this way: each city, village and county still adopts its own code. So a baseline is a minimum, not a replacement for the local edition (Illinois Municipal League, 2025 statewide code baseline).

Rockford

Rockford follows the 2021 ICC code cycle. The 2021 International Residential Code with local amendments took effect January 1, 2025, for permits submitted on or after December 31, 2024. The amendments we could read change two things that touch a basement: permit exemptions (R105.2) and flood elevation (R322.2.1). In a flood hazard area, a basement floor that is below grade on all sides must sit at or above base flood elevation plus one foot, which affects new basements more than a finish of an existing one, though a reviewer will check your flood zone. We found no local change to egress (R310) or ceiling height (R305) in the part of the document that loaded (City of Rockford, Building Codes and Ordinances, City of Rockford, Local Amendments to the 2021 IRC).

Loves Park

Ordinance 4689-25, adopted February 17, 2025, adopts the 2021 International Residential Code as the city residential code. Its amendments cover permit exemptions (R105.2), permit posting (R105.7), work before a permit (R108.6), sprinklers (R313, not required in one- and two-family dwellings, including additions and alterations) and flood elevation (R322). The city also lists the 2014 Illinois Plumbing Code, the 2021 Illinois Energy Conservation Code, the 2020 National Electrical Code with amendments and the 2021 International Building Code as of April 1, 2025 (City of Loves Park, Ordinance 4689-25, City of Loves Park, adopted codes (March 2025)).

Winnebago County

The county codes page, last modified February 20, 2025, says the Building Division follows the 2015 International Residential Code and the 2014 National Electrical Code, among others. Ordinance 2016 CO 034 adopts the 2015 IRC at County Code Sec. 18-321 with amendments we did not retrieve. That listing looks old next to the statewide baseline, so confirm the edition with the Building Division before you design (Winnebago County, Codes and Ordinances, Winnebago County, Ordinance 2016 CO 034 (2015 IRC)). Of the 14 places we cover, 9 are in that county-listed group and 1 had no code edition we could find.

Why the edition matters for a basement

The rules a finished basement runs into most are egress (R310), ceiling height (R305) and the energy code. The model 2021 numbers for those are in the egress guide and the ceiling height guide. If a municipality is on an older edition or has an amendment, a number can move. The energy code is separate: the 2021 Illinois Energy Conservation Code took effect January 1, 2024 for permit applications on or after that date (University of Illinois, Illinois Energy Conservation Code (effective Jan. 1, 2024)), and it has a basement wall insulation row, covered in the insulation guide.

What to ask the permit office

• Which edition of the residential code applies to my permit date?
• Does the city or county amend egress, ceiling height or smoke alarm rules?
• Is the electrical code the 2020 or 2014 National Electrical Code here?
• Is my lot in a flood hazard area?

What the edition changes in practice

Most of the basement rules in this site's guides come from the 2021 International Residential Code, because that is what Rockford and Loves Park state. If your office is on an older edition the headline rules still read alike, but details such as the wording of exceptions, the window well sections and the smoke alarm sections can differ. That is why this site says “the model 2021 numbers” and sends you to the office rather than telling you a number is final. When an office confirms its edition and its amendments, write the answer on your permit drawing so the framer, the electrician and the window installer all work to the same text.

Local amendments worth knowing about

• Permit exemptions (R105.2) differ by municipality. Rockford and Loves Park both exempt repairs to interior wall or ceiling coverings of half or less of a room when no framing is exposed.
• Permit posting (R105.7). Loves Park and Rockford ask for the permit to be visible from the street.
• Work before a permit (R108.6). The penalty rules are in the fee guide.
• Sprinklers (R313). Loves Park says sprinklers are not required in one- and two-family dwellings, including alterations.
• Flood elevation (R322). Both cities amend it for basement floors in flood hazard areas; it affects new basements more than a finish.

Where to go next

This guide sits under Framing and drywall. Every price on this site, with its source and date, is on the basement finishing cost page. If this topic is on your list, these guides cover the neighbouring questions: Do I Need a Permit to Finish a Basement in Illinois?, Basement Permit Office for Every Winnebago County Town, Basement Egress Window Requirements in Illinois, and Basement Wall Insulation in Northern Illinois.